1. Field of the Invention
The present invention relates to a technique of detecting a remaining toner amount in an image forming apparatus like a copying machine or a printer using an electrophotographic system.
2. Description of the Related Art
There is a known image forming apparatus using the electrophotographic system that is provided with a toner remaining amount sensor for detecting a remaining toner amount or existence of toner. There are many methods of detecting the remaining toner amount. One of them is known as an electrostatic capacity method by which the remaining toner amount is detected as electrostatic capacity between electrodes.
The remaining toner amount sensor of the electrostatic capacity method detects the toner remaining amount on the principle that the electrostatic capacity between the electrodes varies with the amount of toner (dielectrics) between the electrodes. Accordingly, when specific inductive capacity ∈t of the toner changes, the different electrostatic capacities are detected for the same remaining toner amount. For example, the specific inductive capacity ∈t of toner changes with humidity and temperature. Since the specific inductive capacity ∈t increases as the moisture content of toner increases, the toner amount that is determined as little under the dry condition may be determined as enough under the absorbed moisture condition.
In view of such a problem, Japanese Laid-Open Patent Publication (Kokai) No. 2002-132038 (JP 2002-132038A) suggests a method of correcting the detected remaining toner amount by reflecting measured environmental conditions, such as temperature and humidity, that become factors of varying the specific inductive capacity ∈t of toner as a method of raising the detection accuracy of the remaining toner amount by the remaining toner amount sensor.
However, the measured environmental condition is not necessarily coincident with the condition of toner. Accordingly, when the measured environmental condition is different from the condition of toner, the remaining toner amount detected by the remaining toner amount sensor in the electrostatic capacity method has an error.